Re: What's so special about objects/17/ ?
- Date: Sun, 7 Oct 2018 20:35:57 +0200
- From: Johannes Sixt <j6t@xxxxxxxx>
- Subject: Re: What's so special about objects/17/ ?
Am 07.10.18 um 20:28 schrieb Ævar Arnfjörð Bjarmason:
In 2007 Junio wrote
+static int need_to_gc(void)
+ * Quickly check if a "gc" is needed, by estimating how
+ * many loose objects there are. Because SHA-1 is evenly
+ * distributed, we can check only one and get a reasonable
+ * estimate.
1. We still have this check of objects/17/ in builtin/gc.c today. Why
objects/17/ and not e.g. objects/00/ to go with other 000* magic such
as the 0000000000000000000000000000000000000000 SHA-1? Statistically
it doesn't matter, but 17 seems like an odd thing to pick at random
out of 00..ff, does it have any significance?
The reason is explained in the comment. And, BTW, you do know about this
one: https://xkcd.com/221/ don't you? (TLDR: the title is "Random Number")
2. It seems overly paranoid to be checking that the files in
.git/objects/17/ look like a SHA-1. If we have stuff not generated by
git in .git/objects/??/ we probably have bigger problems than
prematurely triggering auto gc, can this just be removed as
redundant. Was this some check e.g. expecting that this would need to
deal with tempfiles in these directories that we created at the time
(but no longer do?)?
It's not about that there are SHA-1s in there, it's about how many there